This invention relates to transferring sheet material and in particular to a lightweight vacuum pickup for a shuttle system to transfer hot glass sheets from a furnace to a shaping station.
Shaped and tempered glass sheets are widely used as side or rear windows in vehicles such as automobiles and the like. To be suitable for such applications, flat glass sheets must be shaped to precise, defined curvatures dictated by the shape and outline of the frames defined in the window opening. It is also important that the windows meet stringent optical requirements and that the windows be free of optical defects that would tend to interfere with the clear viewing therethrough.
The commercial production of shaped glass sheets for such purposes commonly includes conveying a flat glass sheet along a substantially horizontal path that extends through a tunnel type furnace to heat the sheet to its softening temperature, shaping the heated glass sheet to a desired curvature and cooling the bent glass sheet in a controlled manner to a temperature below the annealing point of the glass. The glass sheet may be lifted off the conveyor surface by suction using a vacuum pickup and transferred to a shaping station where it is deposited between mold surfaces and pressed to shape, as disclosed in U.S. Pat. Nos. 4,662,925 and 4,666,492 to Thimmons et al., 4,666,493 to Frank et al., 4,666,496 to Fecik et al. and 4,767,434 to Schwartz et al.
In this type of shuttling arrangement, the weight of the pickup is of great concern. Generally, a ceramic block is used for the vacuum pickup and, depending on its size, may weigh upwards of 1,000 lbs. (453 kg). This large weight requires large motors to move the pickup at the speeds required to maintain an efficient shaping cycle. In addition, the excessive weight of the pickup adds to the wear and tear on the motor and other components of the shuttle drive arrangement. Also, accurate positioning of the pickup assembly becomes difficult because of its weight.
It would be advantageous to provide a lightweight vacuum shuttle system for use in a horizontal press bending arrangement to transfer glass into a shaping station that may be moved rapidly and positioned accurately.